Mark a point on a sphere
You could give one or more faces of a sphere a different material (to make the faces smaller subdivide the sphere). Then you could render the scene and press the left mouse button make the coordinates show up.


First add a sphere and two materials with different colors. Then switch to edit mode and change the selection mode to faces.





Now select one or more faces and the second (in this case red) material. Press Assign to assing this material to the selected face. To see the selected material in the 3D view select the shading mode Material.





Render the scene and press the left mouse button on one of the colored points. The (image) coordinates are shown at the bottom left corner of the image view.




Here is an animation of the whole process.